Sample mount for a scanning electron microscope

ABSTRACT

A sample mount and method is disclosed for securing a semiconductor wafer sample to a generic base of a scanning electron microscope. The mount has two opposing clamp members that move relative to one another in response to rotational input to a lead screw. By placing a sample between the clamp members and rotating the lead screw, the samples may be clamped for inspection. When inspection is complete, the lead screw may be rotated in the opposite direction to release the clamping hold on the sample. The clamp members are adjustable to hold varying thicknesses and numbers of specimens making up the sample. In one embodiment, both clamp members move symmetrically from a common origin. In yet another embodiment, one clamp member is fixed relative to the mount and the other clamp member moves relative thereto.

This application is a Continuation of U.S. application Ser. No.09/237,283, filed Jan. 25, 1999 now U.S. Pat. No. 6,414,322 which isincorporated herein.

FIELD OF THE INVENTION

The present invention pertains to electron microscopes. Specifically,this invention pertains to a sample mount for use with a scanningelectron microscope.

BACKGROUND OF THE INVENTION

The semiconductor wafer fabrication process relies heavily on physicalinspection processes to ensure product quality. Due to the minute sizeof the wafer features, highly specialized equipment is required. Thisequipment typically includes a variety of viewing instruments such asmicroscopes which permit a technician to accurately magnify and viewspecific features of the wafer sample.

For various reasons, conventional optical microscopes are ill-fitted forwafer inspection. For example, they are limited in their ability toresolve detail at a level sufficient to enable adequate waferexamination. Additionally, they are unable to achieve the requiredmagnification levels. Furthermore, depth-of-field (i.e., the ability tokeep objects at two different depths simultaneously in focus) isrestricted, requiring the operator to constantly re-focus the microscopeas different areas of the sample are inspected.

These drawbacks are eliminated by using a scanning electron microscope(SEM). Unlike an optical microscope, the SEM utilizes an electron beamto bombard the sample as it sits within a vacuum environment. Due to thecharacteristics of the electron beam (as opposed to the visible lightsource used in optical microscopes), resolution and magnification aresignificantly increased. Additionally, no depth-of-field problems existwith the SEM so surfaces at any depth can be examined withoutre-focusing. These advantages have made the SEM essential to the waferinspection process.

Before viewing the wafer sample in the SEM, the wafer must be securelymounted. Typically, the microscope includes a movable base to facilitatespecimen mounting. However, an appropriate sample mount is necessary tosecure the sample to the base. The sample mount used varies depending onthe wafer features to be inspected. For example, sample mounts are knownfor inspecting the face of the wafer while other mounts permitinspection of wafer edge features. The present invention is addressed tothe latter and the remainder of this discussion is directed accordingly.

One apparatus is described by the Applicant herein in a co-pending,commonly assigned application entitled “Wafer Sample Retainer for anElectron Microscope,” filed on Dec. 01, 1997 having Ser. No. 08/980,932.

For semiconductor wafers, inspection of edge features is usuallyaccomplished by securing several wafers together and mounting the samplein a vertical orientation relative to the SEM. The mount typicallyconsists of a vertical member to which one or more wafer specimens aresecured using a curable adhesive. Copper tape is then wrapped around thespecimens and the mount to secure the sample. While such mounts haveproven effective, drawbacks exist. For example, the application andremoval of the tape adds additional steps to the inspection process.Additionally, the curable adhesive may require several hours to cureprior to inspection. Furthermore, periodic cleaning of the fixture maybe required to remove adhesive residue.

Thus, there are issues concerning increased setup time with currentsemiconductor sample retaining devices. As wafer fabrication facilitiescontinue to increase production rates, the total number of wafersinspected must also increase. As a result, there is a need for a samplemount that provides quick and effective mounting without the drawbacksinherent with adhesives.

SUMMARY OF THE INVENTION

A sample mount for an scanning electron microscope (SEM) is disclosed inwhich the mount comprises a first clamp member, a second opposing clampmember, and a lead screw operatively connected to both clamp members.Rotation of the lead screw varies the distance between the clampmembers. A method for retaining a sample for examination in a SEM isalso disclosed comprising securing a sample mount to a base, inserting asample into the sample mount, and turning a lead screw in a firstdirection to move a first clamp member toward a second clamp member,thereby securing the sample therebetween.

The sample may be a single silicon wafer or a plurality of wafers.Various sample thicknesses may be accommodated by merely turning thelead screw to move the clamp members relative to one another.

The sample mount may be removably mounted to a base on the SEM. The SEMmay further include a rail in which the base is adjustably positionable.The base may be positionable with a motor-driven screw.

In one embodiment, both clamp members are movable relative to the base.In another embodiment, one clamp member is fixed relative to the baseand the other clamp member moves relative thereto.

The sample mount may comprise a retaining assembly having a plate and aclamp body removable attached to the plate. A first and second clampmember may be operatively connected to the retaining assembly wherebythe clamp members are capable of securing a sample therebetween. A leadscrew may be secured to the retaining assembly and operatively connectedto the first and second clamp members, whereby rotation of the leadscrew varies the distance between the clamp members. A thumb-wheel maybe provided at one end of the lead screw to assist the operator inturning the screw. The retaining assembly, first and second clampmembers, and the lead screw may all be removably secured to a base onthe SEM.

In one embodiment, the lead screw may comprise a central threadedportion having a first threaded portion and a second threaded portionwherein the first threaded portion has a right-handed thread and thesecond threaded portion has a left-handed thread. The first clamp memberis threadably engaged to the first threaded portion of the lead screwand the second clamp member is threadably engaged to the second threadedportion such that rotation of the lead screw in a first directionresults in relative closure of the clamp members. Alternatively,rotation of the lead screw in a second direction results in relativeseparation of the clamp members. Regardless, the clamp members moverelative to a common origin.

The present invention provides an improved sample mount that permitsquick and efficient edge mounting of wafer samples within a SEM.Furthermore, mounting is accomplished without the use of messy adhesivesand tapes. By avoiding the use of adhesives, the sample mount does notrequire the lengthy cure time often associated with adhesive mounts.Advantageously, inspection throughput is increased, preventing waferinspection from becoming a production bottleneck.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention described herein will be further characterized withreference to the drawings, wherein:

FIG. 1 is a perspective view of a SEM showing a sample mount inaccordance with one embodiment of the present invention;

FIG. 2 is a diagrammatic perspective view of one exemplary embodiment ofthe sample mount in accordance with the present invention;

FIG. 3 is an exploded perspective view of the sample mount of FIG. 2;

FIG. 4 is a partial section view taken along line 4—4 of FIG. 2 whereinthe clamp body, the clamp plate, the clamp members, and the thumb-wheelare shown in section;

FIG. 5 is an enlarged partial side view of the sample mount of FIG. 2showing the tab and recess;

FIG. 6 is a diagrammatic perspective view of another exemplaryembodiment of the sample mount in accordance with the present invention;and

FIG. 7 is a partial section view taken along line 7—7 of FIG. 6 whereinthe clamp body, the clamp plate, the clamp member, and the thumb-wheelare shown in section.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following detailed description of the embodiments, reference ismade to the accompanying drawings which form a part hereof, and in whichare shown by way of illustration specific embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

FIG. 1 shows a perspective view of one embodiment of a sample mount 10in accordance with the present invention as it would be installed in ageneric scanning electron microscope (SEM) 12. Referring to FIG. 2, asample mounting assembly 11 includes the sample mount 10 and a base 14to which the sample mount 10 is secured. The base 14 is positionablealong a rail 16 and may be externally driven by a drive screw 18operably connected to a drive motor 20. Alternatively, the base 14 maybe manually positionable by a variety of devices known in the art or byhand. By selectively engaging the drive motor, the base 14 may belocated at a point along the rail 16 that provides optimal sampleviewing. The sample mount 10 extends upwardly from the base 14 to retaina wafer sample 22 (shown in FIG. 4) for viewing under the SEM. Thesample may consist of one or more semiconductor wafer specimens of equalor varying thickness.

With this brief overview, attention will now be focused on one exemplaryembodiment of the sample mount 10 of the present invention. Referringgenerally to FIGS. 3-5, the sample mount 10 comprises a plate 24 and aclamp body 26. The plate 24 and clamp body 26 are substantially equal insize and form a generally rectangular shape in the plan view. The clampbody 26 is formed from two identical half-sections 21 and 23. Eachhalf-section includes two threaded holes (not shown) which, whenassembled, are in axial alignment with two of the four fastener holes 27located in the plate 24. When assembled, four flathead cap screws 29(only one of which is shown in FIG. 3) secure the plate 24 to thehalf-sections 21, 23 of the clamp body 26.

Referring particularly to FIG. 3, the plate 24 includes a pair ofopposing tabs 28 extending upwardly from a top side. It is noted thatthe terms “up” and “down” are used throughout the specification only fordescriptive purposes and are not intended to limit the scope of theinvention in any way. Located on the upper surface of each tab 28 is afirst convex radius 30 (best shown in FIG. 5). The purpose of thisradius will become apparent shortly. The clamp body 26 has a pair ofcentrally located opposing recesses 32. Extending between the recesses32 of the clamp body 26 is a centrally located slot 34 having a slotwidth 36. The recesses are designed to receive the tabs 28 when theplate 24 and the clamp body 26 are assembled. While the tabs are shownintegral to the plate 24, it should be noted that the tabs 28 andrecesses 32 could be reversed (i.e., the tab 28 could be integral to theclamp body 26 and the recess 32 could be integral to the plate 24). Suchan arrangement would still be within the scope of the invention. Asshown in FIG. 5, each recess 32 further includes a second convex radius38 substantially equal to the first convex radius 30. The constructionof tabs 28 and recesses 32 are such that, when the bottom plate 24 isassembled with the clamp body 26, the interrelation of the first andsecond convex radii 30, 38 form opposing, generally cylindrical openings40 having a retaining diameter 42. The tabs are spaced apart by a tabseparation 44 best shown in FIG. 4.

Referring once again to FIG. 3, the sample mount 10 additionallycomprises a first clamp member 46 and a second clamp member 48. Theclamp members 46 and 48 are T-shaped members having a first or uppergenerally horizontal portion 50 and a second or lower generally verticalportion 52. The upper horizontal portions 50 form opposing specimenholding faces. Each lower vertical portion 52 has a width 54 slightlysmaller than the slot width 36 so that the lower vertical portion 52 ofthe clamp members 46, 48 slidably nests within the slot 34. Each lowervertical portion 52 also includes a threaded hole 56, 57 whose purposewill become apparent shortly. Thus, the holding faces 50 are held in aparallel relation to one another (best shown in FIG. 2) by the nestingrelationship of the lower vertical portion 52 and the slot 34. However,each clamp member 46, 48 can move toward or away from the other clampmember by merely sliding within the slot 34.

As shown in FIG. 3, a lead screw 58 spans between the cylindricalopenings 40 (see FIG. 5). The lead screw has a central threaded portion60 having a minor thread diameter. At each end of the central threadedportion 60 is a first end portion 64 which is best viewed in FIG. 4. Inthis embodiment, the first end portion 64 comprises a first non-threadedportion 64 having a first diameter 66 which is smaller than the minordiameter of the central threaded portion 60. The central threadedportion 60 and the first non-threaded portions 64 together define ascrew length 62 that is best viewed in FIG. 4. In an alternativeembodiment, the first end portion 64 is merely a continuation of centralthreaded portion 60 such that the central threaded portion 60 extendsover the entire screw length 62. Located immediately adjacent andoutboard to each first non-threaded portion 64 is a second non-threadedportion 68 having a second diameter 70 which is smaller than the firstdiameter 66. The second diameter 70 is slightly smaller than theretaining diameter 42 (see FIG. 5) such that each retaining diameter mayreceive and retain one end of the lead screw 58 by the second diameter70. The lead screw 58 is also restrained from longitudinal motion by theclose fit of the first non-threaded portions 64 and the tabs 28. Thatis, the screw length 62 is slightly smaller than the tab separation 44,thus restricting lead screw motion along the axis of the lead screw.

Extending from one end of the lead screw 58 is an extended portion 72 ofthe second non-threaded portion 68. The extended portion 72 is designedto operatively engage a thumb-wheel 74. In the embodiment shown, thethumb-wheel is secured by a press fit to the extended portion 72 butother securing methods (e.g., threaded engagement, staking, set screw)are also within the scope of the invention. The thumb-wheel ispreferably knurled on its outer diameter to permit easy turning by hand.While the embodiment shown utilizes the thumb-wheel 74, other featuresthat assist in turning the lead screw 58 (i.e., flathead or Phillipsscrew head, splined head, allen head, etc.) are also within the scope ofthe invention.

Referring still to FIGS. 3 and 4, the central threaded portion 60 of thelead screw 58 further comprises a left-hand threaded portion 76 and aright-hand threaded portion 78. When assembled, the left-hand threadedportion 76 threadably engages the threaded hole 56 of the second clampmember 48, which has a left-hand thread, while the right-hand threadedportion 78 threadably engages the threaded hole 57 of the first clampmember 46, which has a right-hand thread. In this way, rotational motionof the lead screw 58 in a first direction causes the clamp members 46,48 to move closer together while rotation of the lead screw in a seconddirection causes the clamp members to separate. The operator may,accordingly, change the distance between the clamp members 46, 48 bymerely turning the thumb-wheel 74. When the thumb-wheel is turned, theclamp members move toward or away from a common origin. Thus, regardlessof variations in sample thickness, the centerline of the sample remains“centered” relative to the base.

The threaded holes 56, 57 and threaded portions 76, 78 are each 6-32 UNCthreads (either left-handed or right-handed as described herein).However, those skilled in the art will realize that other thread sizesand standards are also within the scope of the invention.

Referring once again to FIG. 2, the sample mount 10 may also includes apin 80 extending downwardly from the plate 24. The pin 80 is received bya central opening 82 in the base 14. A socket set screw (not shown) orsimilar fastener may be threadably engaged with the base 14 normal tothe opening 82 to secure the pin 80 relative to the base 14.

Having described the invention in detail, assembly of the sample mount10 will now be described. First, the pin 80 may be pressed into theplate 24, ensuring that it does not protrude beyond an upper surface 81(see FIG. 4) of the plate. Next, both clamp members 46, 48 may bethreaded onto the lead screw 58. Each clamp member 46, 48 should bethreaded to its center-most position (i.e., the clamp faces 50 should be“centered” with respect to the lead screw threaded portion 60). Theclamp members and lead screw together may then be placed into eitherhalf-section 21 (or 23) such that second diameter 70 of one end of thelead screw 58 is retained within the second convex radius 38 and thefirst non-threaded portion 64 is in an abutting relation with an insidesurface of the clamp body 26 (as generally shown in FIG. 4). Thehalf-section 21 may then be loosely fastened to the plate 24 with twofasteners 29. The other half-section 23 (or 21) may then be attached andsimilarly fastened to the plate 24 with the remaining fasteners 29.Finally, half-sections 21, 23 may be aligned relative to one another andthe fasteners 29 may be tightened to an appropriate torque value. Atthis point, the lead screw 58 is retained between the plate 24 and theclamp body 26 by the retaining diameters 42 and the clamp members 46, 48are threadably engaged to the lead screw 58. If not already installed,the thumb-wheel 74 may be attached to the extended portion 72 as shownin FIGS. 2 and 4.

In use, the sample mount 10 is attached to the base 14 by inserting thepin 80 into central opening 82. The mount 10 may be secured with a setscrew (not shown) or other conventional means (e.g., threaded orfrictional engagement). The specimen sample 22 (as shown in FIG. 4) maybe placed between clamp members 46, 48 and the thumb-wheel 74 may berotated in the first direction. As the thumb-wheel is turned, the clampmembers move toward one another until they contact the sample 22. Theclamping force applied to the sample 22 can be varied proportionally tothe amount of torque applied to the thumb-wheel 74. Adjustment of thesample location relative to the SEM can be made by selectivelyenergizing the motor 20 to drive the base 14 within the rail 16.

To release the sample 22 after inspection, the thumb-wheel 74 is simplyrotated in the second direction, thereby releasing the samples from theclamp members 46, 48. A second set of specimens may then be inserted.Due to the combination thread of the lead screw 58, the clamp membersmove toward and away from a common center or origin. Thus, even if asample is of different thickness than the previously inspected sample,the center of the sample is always in the same position relative to thebase. Accordingly, movement of the base 14 along the rail 16 isminimized.

Another exemplary embodiment of the sample mount of the presentinvention is shown in FIGS. 6 and 7. Here, a sample mount 110 is shown.While similar in most respects to the sample mount 10, the sample mount110 differs in that one clamp member defines a fixed (relative to theclamp body) clamp face. That is, the clamp body 126 additionallyincludes an upwardly extending clamp face 148 such that the clamp body126 is a generally L-shaped member. A centrally located slot 134 isdisposed perpendicularly to the clamp face 148 and extends through theclamp body 126. In opposing relationship to the clamp face 148 is agenerally T-shaped clamp member 146 having a first or upper generallyhorizontal portion 150 and a second or lower generally vertical portion152. The upper horizontal portion 150 forms a specimen holding facesimilar to clamp face 148. The lower vertical portion 152 slidably nestswithin the slot 134. The clamp member 146 can move toward or away fromthe clamp face 148 by merely sliding within slot 134. The lower verticalportion 152 also includes a threaded hole 157 through which a lead screw158 passes as shown in FIG. 7.

Referring to FIG. 7, the lead screw 158 is retained in a fashionsubstantially identical to that shown by the lead screw 58 in FIG. 4.However, the lead screw 158 comprises a unitary threaded portion 160instead of the dual thread of the lead screw 58. Like the embodimentdescribed in FIG. 4, the lead screw 158 is retained by a firstnon-threaded portion 164 and a second non-threaded portion 168 locatedat each end of the lead screw. A thumb-wheel 174 is attached to anextended portion 172 of one of the second non-threaded portions 168. Thethumb-wheel 174 is preferably knurled on its outer diameter to permiteasy turning by hand.

When assembled, the threaded portion 160 threadably engages the threadedhole 157 of the clamp member 146. Rotational motion of lead screw 158 ina first direction causes the clamp member 146 to move toward the clampface 148 while rotation of the lead screw in a second direction causesthe clamp member to move away from the face 148. The operator maytherefore change the distance between the clamp member 146 and the clampface 148 merely by turning the thumb-wheel 174.

As with the embodiment shown in FIG. 2, the sample mount 110 shown inFIG. 6 also includes a pin 180 extending downwardly from the plate 124.Preferably, the pin 180 is received by the central opening 82 in thebase 14. A socket set screw (not shown) may be threadably engaged with athreaded hole (also not shown) in the base to secure the pin 180relative thereto.

To assemble the embodiment shown in FIGS. 6 and 7, the clamp member 146is slightly threaded onto the lead screw 158. The opposite end of thelead screw may then be inserted into the slot 134 and the clamp member146 slid toward the clamp face 148 until the opposite end of the leadscrew 158 can also drop through the slot 134. Unlike the embodimentshown in FIGS. 2-5, splitting of the clamp body 126 is not required. Theclamp body 126 may then be attached to a plate 124 and the lead screw158 positioned such that it is retained in a manner substantiallyidentical to that discussed regarding the lead screw 58. Four fasteners(not shown) secure the clamp body 126 to the plate 124. The thumb-wheel174 may then be secured to the extended portion 172 of the lead screw158.

In use, the sample mount 110 is inserted and secured to the base 14.Sample 22 may then be placed between the clamp member 146 and the clampface 148 and the thumb-wheel 174 may be rotated in the first direction.As the thumb-wheel is turned, the clamp member 146 moves toward theclamp face 148 until the sample 22 is sandwiched therebetween. Theclamping force applied to the sample 22 can be varied proportionally tothe amount of torque applied to the thumb-wheel 174. Adjustment of thesample location relative to the SEM can be made by selectivelyenergizing the motor 20 to drive the base 14 within the rail 16.Alternatively, the mount 110 may be rotated within the base.

To release the sample after inspection, the thumb-wheel is simplyrotated in the second direction, thereby releasing the sample 22 fromthe clamp member 146 and clamp face 148. A second sample may then beinserted and aligned for inspection.

CONCLUSION

The present invention provides an improved sample mount that permitsquick and efficient edge mounting of wafer samples within a SEM.Furthermore, mounting is accomplished without the use of messy adhesivesand tapes. By avoiding the use of adhesives, the sample mount does notrequire the lengthy cure time often associated with adhesive mounts.Advantageously, inspection throughput is increased, preventing waferinspection from becoming a production bottleneck.

In the embodiments herein represented, all components are made from 300series stainless steel. This material was selected for its excellentcorrosion and chemical resistance. Nonetheless, other materials are alsoconsidered to be within the scope of the invention.

Exemplary embodiments of the present invention are described above.Those skilled in the art will recognize that many embodiments arepossible within the scope of the invention. Variations, modifications,and combinations of the various parts and assemblies can certainly bemade and still fall within the scope of the invention. Thus, theinvention is limited only by the following claims, and equivalentsthereto.

I claim:
 1. A sample mount for an electron microscope comprising: afirst clamp member; a second opposing clamp member, the clamp membersadapted for securing a sample therebetween; and a third memberoperatively connected to both clamp members, whereby movement of thethird member varies the distance between the clamp members.
 2. A samplemounting assembly for an electron microscope comprising: a base havingan opening therein; and a sample mount removably connected to the base,the sample mount having: a first clamp member; a second opposing clampmember, the clamp members for securing a sample therebetween; and athird moving member operatively connected to the first and second clampmembers, whereby rotation of the third moving member varies the distancebetween the clamp members.
 3. The mounting assembly of claim 2 furthercomprising a rail, the base adjustable with respect to the rail.
 4. Themounting assembly of claim 2 further comprising means to retain thesample mount within the base.
 5. The mounting assembly of claim 4wherein the retaining means comprises a pin disposed on the sample mountwherein the opening on the base receives the pin when the sample mountis connected to the base.
 6. The mounting assembly of claim 2 whereinthe third moving member additionally comprises means to assist in movingthe third moving member.
 7. The mounting assembly of claim 2 wherein thefirst clamp member moves relative to the base, and the second clampmember moves relative to the base.
 8. The mounting assembly of claim 2wherein one of the first clamp member and the second clamp member isfixed relative to the base, and, wherein the other of the first clampmember and the second clamp member moves relative to the base.
 9. Asample mount for retaining a sample for viewing with an electronmicroscope comprising: a retaining assembly comprising: a plate having afirst side and a second side; and a clamp body having a first side and asecond side, the first side of the clamp body being removably attachedto the first side of the plate; a first clamp member coupled to theretaining assembly; a second opposing clamp member coupled to theretaining assembly, the clamp members adapted to retain the samplebetween the first clamp member and the second clamp member; and a thirdmoving member secured to the retaining assembly and engaged with atleast one of the first clamp member and the second clamp member.
 10. Asample mount for retaining a sample for viewing with an electronmicroscope comprising: a retaining assembly comprising: a plate having afirst major surface and a second major surface; and a clamp bodyincluding: a first portion; and a second portion, the first portion ofthe clamp body and the second portion of the clamp body being removablyattached to the first major surface of the plate; a first clamp memberconnected to the retaining assembly; a second clamp member connected tothe retaining assembly, the clamp members for selectively retaining thesample between the first clamp member and the second clamp member; athird clamp engaging member secured to the retaining assembly andthreadably engaged with the first clamp member and the second clampmember; and a pair of opposing tabs attached to the plate, the pair ofopposing tabs extending outward from the first major surface of theplate, the pair of opposing tabs separated by a tab separation.
 11. Thesample mount of claim 10 wherein each tab of the pair of opposing tabsincludes a first convex radius surface.
 12. The sample mount of claim 11wherein the first clamp member has a first recess therein for receivingone tab of the pair of opposing tabs and wherein the second clamp memberhas a second recess therein for receiving the other of the pair ofopposing tabs, wherein the first recess has a second convex radiussurface substantially equal in size to the first convex radius surfaceassociated with one of the pair of opposing tabs and wherein the secondrecess has a second convex surface substantially equal in size to thefirst convex radius surface associated with the other of the pair ofopposing tabs, such that when the plate is attached to the clamp body,the interrelation of the first and second convex surfaces define a pairof opposing cylindrical openings, the opposing cylindrical openingshaving a retaining diameter.
 13. The sample mount of claim 12 whereinthe clamp body has a slot therein between the first recess and thesecond recess.
 14. The sample mount of claim 13 wherein the first clampportion of the clamp body is a first half of the clamp body and, whereinthe second clamp portion of the clamp body is a second half of the clampbody.
 15. The sample mount of claim 14 wherein the first half of theclamp body is separable from the second half of the clamp body along aline substantially perpendicular to the slot.
 16. A sample mount forretaining a sample for viewing with an electron microscope comprising: aretaining assembly comprising: a plate having a first major surface anda second major surface wherein the first major surface includes a pairof opposing tabs extending away from the first major surface and eachtab has a first convex radius, the pair of opposing tabs spaced apart bya tab separation; and a clamp body having a first major surface and asecond major surface, the first major surface of the clamp body beingremovably attached to the first major surface of the plate, wherein thefirst major surface of the clamp body defines a pair of opposingrecesses for receiving the pair of opposing tabs, each recess having asecond convex radius substantially equal in size to the first convexradius of the each of the pair of opposing tabs, such that when theplate is attached to the clamp body, the interrelation of the first andsecond convex radii define a pair of opposing cylindrical openings, theopenings having a retaining diameter, and wherein the clamp body has aslot therein extending generally between the pair of opposing recesses,the slot having a slot width; a first clamp member operatively connectedto the retaining assembly; a second opposing clamp member operativelyconnected to the retaining assembly, the first clamp member and thesecond clamp members each having a first portion and a second portion,the second portion having a width slightly less than the slot width suchthat the second portion of each of the first clamp member and the secondclamp member nests within the slot of the clamp body, wherein the secondportion of the first clamp member has a first threaded opening therein,and the second portion of the second clamp member has a second threadedopening therein, wherein one of the first threaded opening or the secondthreaded opening has a right-handed thread, and the other of the firstthreaded opening or the second threaded opening has a left-handedthread; and a third clamp engaging member secured to the retainingassembly and threadably coupled to the first and second threadedopenings.
 17. The sample mount of claim 16 wherein the clamp body isseparable into a first half and a second half.
 18. The sample mount ofclaim 16 wherein the third clamp engaging member comprises: a centralthreaded portion having a minor diameter; a first end portion at eachend immediately adjacent to the central threaded portion wherein thefirst end portion and the central threaded portion together define ascrew length which is slightly less than the tab separation; and asecond non-threaded portion located immediately outboard of each firstend portion, the second non-threaded portion having a second diameter.19. The sample mount of claim 18 wherein the first end portion defines afirst non-threaded portion having a first diameter.
 20. The sample mountof claim 19 wherein the first diameter is less than the minor diameter,and the second diameter is less than the first diameter and is also lessthan the retaining diameter such that, when installed in the retainingassembly, the second non-threaded portion is retained within the opposedcylindrical openings, permitting rotation of the third clamp engagingmember but restraining it from longitudinal motion.
 21. The sample mountof claim 20 wherein the central threaded portion of the third clampengaging member further comprises a first threaded portion having aright-banded thread threadably engaged with one of the first threadedopening of the first clamp member or the second threaded opening of thesecond clamp member, and a second threaded portion having a left-handedthread threadably engaged with the other of the first threaded openingof the first clamp member or the second threaded opening of the secondclamp member, whereby rotation of the lead screw in a first directionresults in relative closure of the clamp members and rotation of thelead screw in a second direction results in relative separation of theclamp members.
 22. The sample mount of claim 16 wherein the clampmembers move toward and away from a common origin.
 23. The sample mountof claim 16 further comprising a thumb-wheel secured to the third clampengaging member.
 24. The sample mount of claim 16 wherein the retainingassembly, first and second clamp members, and the third clamp engagingmember are removably secured to a base.
 25. A sample mount for use withan electron microscope comprising: a retaining assembly comprising: aplate having a first side and a second side; and a clamp body having afirst side and a second side, the first side of the clamp body beingremovably attached to the first side of the plate and the second side ofthe clamp body defining a fixed clamp face; a clamp member connected tothe retaining assembly; and a third clamp engaging member secured to theretaining assembly and connected to the clamp member.
 26. A sample mountfor use with an electron microscope comprising: a retaining assemblycomprising: a plate having a first major surface and a second majorsurface; and a clamp body having a first major surface and a secondmajor surface, one of the first major surface of the clamp body and thesecond major surface of the clamp body being removably attached to thefirst major surface of the plate, and the other of the first majorsurface of the clamp body and second major surface of the clamp bodydefining a fixed clamp face; a clamp member connected to the retainingassembly; and a third clamp engaging member secured to the retainingassembly and connected to the clamp member, wherein the plate furthercomprises a pair of opposing tabs extending away from the first majorsurface of the plate, the pair of opposing tabs being spaced from oneanother.
 27. The sample mount of claim 26 wherein each tab includes afirst convex radius.
 28. The sample mount of claim 27 wherein the one ofthe first major surface of the clamp body and the second major surfaceof the clamp body being removably attached to the first major surface ofthe plate defines a pair of opposing recesses for receiving the pair ofopposing tabs, each of the pair of recesses having a second convexradius substantially equal to the first convex radius such that when theplate is connected to the clamp body, the interrelation of the first andsecond convex radii define a pair of opposing cylindrical openings. 29.The sample mount of claim 28 wherein the clamp body has a slot thereinbetween the opposing recesses, the slot having a slot width.
 30. Thesample mount of claim 29 wherein the clamp member has a first portionsubstantially identical in size and in opposing relation to the clampface, and a second portion, the second portion having a widthdimensioned to nest within the slot of the clamp body.
 31. The samplemount of claim 30 wherein the second portion of the clamp member has athreaded opening therein.
 32. A sample mount for use with an electronmicroscope comprising: a retaining assembly comprising: a plate having afirst side and a second side wherein the first side comprises a pair ofopposing tabs extending away from the first side and each tab has afirst convex radius, the tabs spaced apart by a tab separation; and aclamp body having a first side and a second side, the first side of theclamp body being removably attached to the first side of the plate andthe second side of the clamp body defining a fixed clamp face, whereinthe first side of the clamp body defines a pair of opposing recesses forreceiving the tabs, each recess having a second convex radiussubstantially equal in size to the first convex radius such that whenthe plate is attached to the clamp body, the interrelation of the firstand second convex radii define a pair of opposing cylindrical openings,the openings having a retaining diameter, and wherein the clamp body hasa slot therein between the opposing recesses, the slot having a slotwidth; a clamp member attached to the retaining assembly wherein theclamp member has a first wider portion in opposing relation to the clampface, and a second portion having a width slightly less than the slotwidth, the second portion of the clamp member nesting within the slot ofthe clamp body, the second portion of the clamp member having a threadedopening therein; and a clamp engaging member secured to the retainingassembly and operatively connected to the clamp member.
 33. The samplemount of claim 32 wherein the clamp engaging member comprises: a centralthreaded portion having a minor diameter; a first end portion located ateach end immediately adjacent to the central threaded portion whereinthe first end portion and the central threaded portion together define ascrew length which is less than the tab separation; and a secondnon-threaded portion located immediately outboard of each first endportion, the second non-threaded portion having a second diameter. 34.The sample mount of claim 33 wherein the first end portion defines afirst non-threaded portion having a first diameter.
 35. The sample mountof claim 34 wherein the first diameter is less than the minor diameterand the second diameter is less than the first diameter and is also lessthan the retaining diameter such that, when installed in the retainingassembly, the second non-threaded portion is retained within the opposedcylindrical openings, permitting rotation of the lead screw butrestraining the lead screw from longitudinal motion.
 36. The samplemount of claim 35 wherein the central threaded portion is threadablyengaged with the threaded opening of the second portion of the clampmember, whereby rotation of the lead screw in a first direction resultsin movement of the clamp member towards the clamp face and rotation ofthe lead screw in a second direction results in movement of the clampmember away from the clamp face.
 37. The sample mount of claim 32further comprising a thumb-wheel attached to at least one end of theclamp engaging member.
 38. A sample mount for an electron microscopecomprising: a first clamp member; a second opposing clamp; and a clampengaging member operatively connected to both the first clamp member andthe second clamp member, whereby rotation of the clamp engaging membervaries the distance between the clamp members.
 39. A sample mountingassembly for an electron microscope comprising: a base having an openingtherein; and a sample mount removably connected to the base, the samplemount having: a first clamp member; a second opposing clamp member; anda clamp engaging member operatively connected to the first and secondclamp members, whereby rotation of a lead screw varies the distancebetween the first clamp member and the second clamp member.
 40. A methodof retaining a sample for examination in an electron microscopecomprising: securing a sample mount to a base; inserting a sample intothe sample mount; and moving a clamp engaging member of the sample mountin a first direction to move a first clamp member toward a second clampmember.
 41. The method of claim 40 further comprising moving a clampengaging member in a second direction to move the first clamp memberaway from the second clamp member.
 42. A method of retaining a samplefor examination in an electron microscope comprising: securing a samplemount to a base; inserting a sample into the sample mount; and moving aclamp engaging member in a first direction to move both a first clampmember and a second clamp member toward the sample.
 43. The method ofclaim 42 further comprising moving a clamp engaging member in a seconddirection to move both the first clamp member and the second clampmember away from the sample.
 44. A sample mount for an electronmicroscope comprising: a first clamp member; a second opposing clampmember, the clamp members sized and shaped to secure a sampletherebetween; and a clamp engaging member connected to both clampmembers, whereby movement of the clamp engaging member varies thedistance between the clamp members.